Plastic sheet cutter with magnetic means to retain lead end of work in grasping position



Jan. 8, 1963 F. J. BRACEY ETAL 3,072,000

PLASTIC SHEET CUTTER WITH MAGNETIC MEANS TO RETAIN LEAD END OF WORK IN GRASPING POSITION Filed Nov. 29, 1961 t hice B Patented Jan. 8, 1953 PLASTHC SHEET CUTTER WITH MAGNETIC lvfEANS T RETAEN LEAD END 0F WRK 1N GRASillNG POSEIN Frederick Il. Bracey, West Acton, and Andre Commeyras,

Concord, Mass., assigner-s to W. R. Grace & Co., Cambridge, Mass., a corporation of Connecticut Filed Nov. 29, 1961, Ser. No. 155,733 5 Claims. (Cl. 83--112) This invention relates to a machine for cutting plastic film and more particularly to a device known as a sheeter which is commonly used for cutting the variable lengths of film which are used in retail lfood packaging.

The thin film which is used yfor packaging retail cuts of meat and other foodstuffs has proved difficult to handle. It is limp, oppy, and sometimes flies out of the way and sticks to itself or to parts of the sheeter in such a manner that considerable groping is necessary before the operator can grasp the film and draw out the proper length to be cut olf.

The present machine spreads the film smoothly, holds the web end of the film securely, and allows a short length of the web end to drape in a position where it may be easily grasped by the operator when the next length of nlm is to be drawn out and cut off. It permits a more expeditious operation of the sheeter since the film is always presented in a convenient position. Time which has been wasted in groping ,for lost-ends is saved by the device.

The device may be understood from the specification and from the drawing in which FIGURE 1 is a front elevation of the machine. FIGURE 2 is a right side elevation.

The machine l comprises a base 11 having two attached side frame members 12 and 13. The side frames are braced by the truss rods 14, 15, and 16. Each side frame carries an integral bracket 17 having an upwardly facing slot 18, designed to receive the shaft 19 which supports the supply roll 21. Rock shaft 22 extends transversely across the machine and projects a short distance beyond each side frame. Shaft 22 is journalled in the bearings 23 and 24 which are fastened to the side frames 1?. and 13. Arms 25 and 26 'are pinned to the rock shaft 22, near each end of the shaft. The arms extend toward the front of the machine and are joined at their extremities by the transverse cutter bar 27. Cutter bar 27 car es a longitudinal slot Z8 cut in its lower face. Coil spring 31, one end of which engages the base l1, and the other engages a collar 3i?. fastened to the rock shaft 22, urges the arms upwardly until they engage the stop bumpers 33 and 34 which are fastened to the side frames 12 and 13. Two more arms 35 and 36 extending to the front of the machine are freely journalled on the rock shaft 22. The ends of arms 35 and 36 are joined by a transverse bar 37 which carries on its upper surface a layer of magnetic rubber 38. The armature 39 `for this rubber magnet is a steel strip having its end portions bent at 90 and slotted. Ends 42 are adjustably secured in bosses 43--43 formed on the arms 25 and 26, by the screws 44 44.

Lever arm 45 is pinned at a point on the rock shaft 22 intermediate between the two side frames. lts end, which extends toward the rearof the machine, terminates in a link 46 lwhich is connected to the piston 47 of an air cylinder 48. Micro-switch 49 is so placed that its button 51 is engaged by the lever -arm 45 when the arm is in its raised position and the cuter bar y27 has consequently completed its downward stroke.

Runaway and coasting of the supply roll 21 is prevented by the brake 52 which engages brake drum 53 which is fastened to the supply roll shaft 19. Brake 52 is pinned to the connecting link 54 which in turn is pinned to brake lever arm 55. -Arm 55 is pivoted at 56 on an upward extension of the side frame 12. The brake 52 is urged into engagement ywith the drum 53 by the pull spring 57 which extends between fra-me 12 and brake lever arm 55.

The actual cutting member is a knife 58, which is `fastened lby appropriate means in a gutter 59, which is for-med along the front of the machine. Knife 58 does not extend above the top of base 11 and consequently at no time can the knife come in contact with the hands of the operator.

The operation of the machine 'is as follows: when viewed from the right side of the machine, the supply roll unwinds counter-clockwise. The lm web W is led upwardly and `over a free-running roller 61 which extends from the extremity of brake lever arm 55 to a companion arm 62 similarly located and pivoted on the side frame 13. =Arrn 62 is not equipped with a brake mechanism. From the roller 611 the film web W passes downwardly between the side frame members and under the spreader bar 63, then forwardly beyond the front of the machine. When a sufficient length of film has been drawn tout, the operator touches a button which is located Iat any convenient position on the work table. The button completes an electrical circuit to a quick-acting electro-pneumatic valve which adm-its air to the lower end of air cylinder 48. Piston 47 therefore rises, pulling arm 45 upwardly and forcing the cutter bar downwardly over the knife 53, thereby severing the film. When lever arm 45 touches the button 51 of the micro-switch 49, an electric circuit to the electro-pneumatic valve is completed which exhausts the air from beneath the piston and permits the spring 31 to raise the cutter bar. The air cylinders, electro-pneumatic valves, and the electrical connections are conventional and will not be further described.

Meanwhile the rubber magnet 3S, which is separated from the armature 39 only by the thickness of the film, clings to its armature and rises `as the cutter bar and its supporting arms return to the raised position. The length of web extending between the spreader bar 63 and the magnet consequently rises and a short length which represents the distance between the magnet 38 and the knife 58 drapes itself downwardly where it can be reached easily by the operator when the next piece is to be withdrawn.

When the operator grasps the exposed end, the pull is momentarily resisted before lthe brake 52 is released. Consequently, a small downward force is developed which is sufficient to overcome the gripping action of the -rnagnet to its armature and the magnet drops to its rest position on the ybase 11 where it is out of the way as the next length of film is withdrawn. The strength of the magnet 38 should be adjusted to a value which will permit the easy release of the magnet when the lm is pulled. lf the magnetic force is too strong, some diniculty ywill be experienced in releasing the film. This degree of magnetic attraction between the `magnet 33 and armature 39 requires for successful operation, that the movement of the cutter -bar assembly be smooth and bounce free. For this reason, air operation of the device is preferred. The exhaust from air cylinder 48 can be easily adjusted to give va dash-pot effect which prevents any bounce and chatter of the cutter bar assembly `from appearing. lf bounce does occur, the forces which are developed are frequently in excess of the magnetic holding force. The result is that the end of the web is no longer held in proper position and may become lost. If other power means are used, for example a solenoid, a dash pot or an equivalent damping device is necessary t0 secure the smooth operation of the cutter bar assembly.

Although it is not absolutely necessary, it is strongly recommended that the magnet 3S be of the so-called rubber magnet type. Metallic magnetic elements can be used, but they occasionally scratch and damage the film. Not only does the soft yielding nature of a rubber magnet prevent any damage to the lm, but it has the advantage that its operation is entirely silent.

We claim:

1. A film sheeting device wherein a film web is cut by a descending cutter bar, an armature mounted for movement with the bar, a freely floating magnet normally disposed Ibeneath said armature and ,below the path of said web and pivotally mounted for compiementary movement with said armature, whereby the armature and magnet close on the web end of the lm when the film is cut and lift the tilm as the bar returns to its raised position, the magnet being releasable from its web-lifting position by pull exerted upon the lm.

2. A device as claimed in claim l wherein the magnet is a strip of flexible magnetic material.

3. A device as claimed in claim l lwherein the advance of the lm by pulling it is initially resisted by a film braking mechanism until the force developed is sufiicient to release the magnet from its film-clamping position.

4. A nn sheeting device wherein a web of fiim is cut by the downward stroke of a cutter-bar Isupported by pivoted arms, having means to lift and to hold the end of the web, comprising a magnet positioned lbelow the path of said web and parallel to and rearwardly spaced from the cutter-bar and carried by free-oating arms having a common pivot axis with the support arms of the cutter-bar, an armature cooperating with the magnet extending between the cutter-bar support arms, means rotatably to support a supply roll, roll braking means, and pull-actuated brake-releasing means, the said device being arranged to clamp the web between the magnet and the armature when the cutter-bar is in film cutting position and then raise the web to a convenient position to be grasped by the operator when the bar returns to its raised position, pull on the web first causing the break-away of the `magnet from its armature and then causing the release of the brake to permit the advance of the film.

5. A web lm sheeting device comprising a base, side frame members attached to the base, means to support a web of film between the side frame members, releasable braking means associated with the support, a cutterbar extending transversely between the side frames supported by arms attached to a shaft extending between the side frames, a magnet disposed beneath the path of said web and extending between the side frames supported by arms having a common pivot axis with the bar snpport arms, an armature extending between and carried by the bar support arms, power means to rock the shaft to thereby Iforce the bar into film-cutting position, a fixed knife cooperating with the cutter-bar, spring means to return the bar to its raised position, said power means including means to damp chatter and bounce of the bar assembly, the magnet land the armature cooperating to clamp the web end of a lrn lbetween them and raise the film to a film-grasping position, said magnet being releasable to pull exerted on the lm.

No references cited. 

1. A FILM SHEETING DEVICE WHEREIN A FILM WEB IS CUT BY A DESCENDING CUTTER BAR, AN ARMATURE MOUNTED FOR MOVEMENT WITH THE BAR, A FREELY FLOATING MAGNET NORMALLY DISPOSED BENEATH SAID ARMATURE AND BELOW THE PATH OF SAID WEB AND PIVOTALLY MOUNTED FOR COMPLEMENTARY MOVEMENT WITH SAID ARMATURE, WHEREBY THE ARMATURE AND MAGNET CLOSE ON THE WEB END OF THE FILM WHEN THE FILM IS CUT AND LIFT THE FILM AS THE BAR RETURNS TO ITS RAISED POSITION, THE MAGNET BEING RELEASABLE FROM ITS WEB-LIFTING POSITION BY PULL EXERTED UPON THE FILM. 